1. Field of the Invention
The present invention relates to a semiconductor device and a band gap reference power supply utilizing the same.
2. Description of the Background Art
In obtaining a reference voltage with high stability and small variation against temperature in a semiconductor integrated circuit, a circuit system called "band gap reference power supply" employing a bipolar transistor is often used. The band gap reference power supply circuit, which has been introduced by R. J. Widlar in 1971 ("New Developments in IC Voltage Regulators" R. J. Widlar, IEEE J. Solid-State Circuits, SC-6, 2-7 (February, 1971)) utilizes the physical characteristics of base-emitter voltage of a silicon transistor when biased in the forward direction as shown in FIGS. 8 and 9. In general, a temperature coefficient of the base-emitter voltage of a transistor is about -2 mV/.degree.C., and then the base-emitter voltage is about 1.2 V in absolute zero point, which is almost equal to a band gap voltage (energy gap, 1.12 V when Ta=300.degree. K.). Adding a voltage proportional to the absolute temperature to the base-emitter voltage of the transistor makes an output voltage of the band gap reference power supply. It is possible to make the temperature coefficient almost zero by controlling the voltage to be added so that the output voltage should be 1.2 V, thereby obtaining an output voltage with
extremely small temperature dependency. Such a system is called "band gap reference power supply".